The present invention relates to novel compounds useful as sunscreen agents, which compounds have ability to absorb sunlight in both the UVA and UVB wavelength range. The present invention further relates to novel skin protection compositions which are effective at protecting skin from both UVA and UVB wavelength sunlight. Finally, the present invention also relates to methods for protecting the skin from the effects of UVA and UVB wavelength irradiation, such as sunburn and sun-induced aging of the skin.
The damaging effects of sunlight on skin are well documented. In spite of this, people are forced to be in the sun for long periods of time due to their occupations. Others are in the sun for long periods through their leisure time activities and/or a desire to have a tanned appearance.
The major short term hazard of prolonged exposure to sunlight is erythema (i.e., sunburn). The 290 to 320 nanometer wavelength ultraviolet radiation range, which is designated by the cosmetic industry as being the "UVB" wavelength range, is the most effective type of UV radiation for producing erythema. The 320 to 400 nanometer wavelength ultraviolet radiation range, which is designated by the cosmetic industry as being the "UVA" wavelength range, also produces erythema.
In addition to the short term hazard of erythema caused by UVA and UVB sunlight, there are also long term hazards associated with this UV radiation exposure. One of these long term hazards is malignant changes in the skin surface. Numerous epidemologic studies have been conducted, and the results demonstrate a strong relationship between sunlight exposure and human skin cancer. Another long term hazard of ultraviolet radiation is premature aging of the skin. This condition is characterized by wrinkling and yellowing of the skin, along with other physical changes such as cracking, telangiectasis (spider vessels), solar keratoses (growths), ecchymoses (subcutaneous hemorrhagic lesions), and loss of elasticity. The adverse effects associated with exposure to UVA and UVB wavelength radiation are more fully discussed in DeSimone, "Sunscreen and Suntan Products", Handbook of Nonprescription Drugs7th Ed, Chapter 26, pp. 499-511 (American Pharmaceutical Association, Washington, D.C.; 1982); Grove and Forbes, "A Method for Evaluating the Photoprotective Action of Sunscreen Agents Against UV-A Radiation", International Journal of Cosmetic Science, 4, pp. 15-24 (1982); and U.S. Pat. No. 4,387,089, to DePolo, issued Jun. 7, 1983; the disclosures of all of which are incorporated herein by reference. Hence, although the immediate effects of ultraviolet radiation may be cosmetically and socially gratifying, the long-term effects are cumulative and potentially serious.
Sunscreen compositions comprising mixtures of molecules which absorb at different UV wavelengths and which thereby protect the skin are known in the art. For example, U.S. Pat. No. 4,264,581, to Kerkhof et al (issued Apr. 28, 1981), discloses a sunscreen composition containing a mixture of 2-ethylhexyl dimethyl-para-amino benzoate and 2-hydroxy-4-methoxy-benzophenone; U.S. Pat. No. 3,751,563, to Richardson (issued Aug. 7, 1973), discloses a sunscreen composition containing a mixture of 2-ethoxyethyl para-methoxycinnamate, amyl para-dimethylamino benzoate, homomenthyl salicylate, and 2-hydroxy-4-methoxy-benzophenone; and U.S. Pat. No. 3,636,077, to Stauffer (issued Jan. 18, 1972), discloses sunscreen compositions containing salts of 5-benzoyl-4-hydroxy-2-methoxy benzene sulfonic acid and 4-aminobenzoic acids or esters.
Notwithstanding the foregoing developments, there remains a continuing need to identify new compounds and compositions which are effective for protecting the skin from ultraviolet radiation in both the UVA and UVB radiation ranges. It is accordingly an object of the present invention to provide compounds which are effective sunscreening agents for both UVA and UVB radiation, as well as sunscreen compositions containing these sunscreen compounds. It is a further object of the present invention to provide methods for protecting the skin of humans or lower animals from the effects of exposure to UVA and UVB wavelength radiation by employing sunscreening compounds and compositions of the present invention.
It is a further object of the present invention to provide sunscreening agents and compositions which are not readily absorbed by the skin; which have increased sunscreen protection and decreased chance for allergy, irritation, or toxicity problems resulting from use; and which are resistant to rub off. A still further object is to provide sunscreen agents and compositions which provide a constant and even protection against both UVA and UVB radiation; which are cosmetically acceptable; and which are readily formulated into sunscreen compositions.
These and other objects will become readily apparent from the detailed description which follows.